The invention relates to an electronic AC voltage switch according to claim 1.
In order to switch large AC voltages (e.g. 60 V) or high AC currents (greater than 1 A), use is primarily made of mechanical AC voltage switches. However, since electronics have successfully been adopted in numerous sectors, thus including the automotive sector, there is a need to develop electronic AC voltage switches for high powers.
The invention is based on the object, therefore, of providing an electronic AC voltage switch which is designed for high powers and can be operated with the least possible energy.
The invention solves this technical problem by means of the features of claim 1.
Charge-dependent MOS transistors which can be driven without any power are appropriate for this purpose. According to the invention, the electronic AC voltage switch has two series-connected MOS transistors, such that the latter can block and transmit an applied AC voltage. In other words, the series-connected MOS transistors can be controlled to assume a high-impedance state and a low-impedance state. At least one device for storing charges is connected to the gate connections of the MOS transistors. Furthermore, a charge feeding device is assigned to each charge storage device for applying a predetermined quantity of charge to the charge storage devices, which corresponds to a first switching state, and for removing a predetermined quantity of charge from the charge storage devices, which corresponds to a second switching state.
Advantageous developments are specified in the subclaims.
In order to be able to produce an electronic AC voltage switch cost-effectively, it is possible to have recourse to componentsxe2x80x94known per sexe2x80x94which are constructed with a floating gate as charge storage device, such as a floating gate field-effect transistor for example. In this case, the floating gate is embedded in an oxide, so that it serves as a charge store for charges which are applied by way of the tunnel effect for example. Floating gate field-effect transistors are used, inter alia, in large numbers as memory cells in electrically erasable programmable read-only memories (EEPROMs). In this way, the switching state of the electronic AC voltage switch can be held or stored even without the permanent application of an external voltage source.
In one embodiment, two MOS transistors of the n-channel type are connected in series in opposite directions such that the source connections of the MOS transistors form the connecting terminals of the electronic AC voltage switch. Accordingly, the MOS transistors have a common drain connection. Furthermore, each MOS transistor is assigned a separate floating gate which is respectively assigned a charge feeding device.
In order to be able to further simplify the construction of the AC voltage switch and thus to reduce the production costs, two n-type MOS transistors are connected in series such that the drain connections of the MOS transistors form the connecting terminals of the electronic AC voltage switch. As a result, the MOS transistors have a common source connection and can be produced with a common oxide. Accordingly, it is also the case that only one charge feeding device is required.
Customary voltage sources which can be connected externally can be used as charge feeding devices.
However, since only small quantities of charge are necessary for switching the electronic AC voltage switch in MOS technology and the duration of the switch-on processes is insignificant, it is possible to use charge feeding devices which only generate small currents.
Such a device may be designed as an optoelectronic component which converts incident light into an electric current.
By way of example, the optoelectronic component comprises at least one first photodiode, such as e.g. a PIN diode, having a first wavelength-dependent sensitivity, and at least one second photodiode connected in parallel with the first photodiode and having a second wavelength-dependent sensitivity, the first photodiode and the second photodiode being connected with opposite polarity. Depending on the wavelength of the incident radiated light, charges are applied to the floating gates or removed therefrom and the switching state of the electronic AC voltage switch is thus defined. Laser diodes or LEDs which generate light at the corresponding wavelengths can be used as light sources. By using photodiodes as charge feeding devices, it is possible to produce the electronic AC voltage switch together with the charge feeding device as an integrated module.
As an alternative, the charge feeding device can also be embodied by a mechanical/electrical device comprising a number of piezoelectric elements for example. The piezoelectric elements are connected in parallel with one another and with opposite polarity and are connected in series with the MOS transistors. Two zener diodes which are connected in opposite directions are connected in parallel with the piezoelectric elements for the purpose of voltage limiting and thus for the purpose of protecting the gate. In this embodiment, the switching state of the AC voltage switch is controlled by mechanical deformation of one of the two piezoelectric elements.
The switching state is controlled as follows: charges pass to the floating gates as a result of mechanical pressure on one piezoelectric element, and charges are removed from the floating gates as a result of the action of force on the other piezoelectric element.
This possibility for supplying charge is in turn opened up by the low demand of the electronic AC voltage switch for charge carriers. A piezoelectric element can only provide very small currents, but this is sufficient for this application.